Aircraft may be equipped with communication, navigation, and surveillance (CNS) systems. With respect to communication systems, the aircraft may be equipped with more than one communication system through which a pilot and/or passengers may communicate with those not located inside the aircraft. Three of these communication systems that are commonly used today include a high frequency (HF) system(s) operable in the frequency band between 2 and 30 megahertz (MHz), very high frequency (VHF) system(s) operable between 118 MHz and 137 MHz, and satellite communication (SATCOM) system(s) operable in L-band, Ku-band, or Ka-band.
Referring now to FIGS. 1 and 2, an exemplar of an aircraft communication network 100 is illustrated. The network 100 may include one or more remote HF systems 110 and 112; one or more remote VHF systems 114, 116, and 118; a remote SATCOM system 120; and an audio management unit (AMU) 122. In some embodiments, the network 100 may be configured with two remote HF systems, three remote VHF systems, and one remote SATCOM system. In some embodiments, the network 100 may be configured with a different number of HF systems, VHF systems, and/or SATCOM systems. In some embodiments, one or more of these systems could be absent.
The HF1 and HF2 systems 110 and 112 could include a plurality of units configured to facilitate two-way, long-range communications between the aircraft and, for example, one or more other aircraft and/or one or more ground stations. In some embodiments, the HF1 system 110 could include an HF1 XCVR 110-1, an HF2 coupler 110-2, and an HF1 antenna 110-3. The HF2 system 112 could include a HF2 XCVR 112-1, an HF2 coupler 112-2, and the HF2 antenna 110-3. As shown, the HF1 system 110 and the HF2 system 112 may employ the same HF1/HF2 antenna 110-3.
As observed, coax cable could be a communication medium through which RF signals may be transmitted and received between the XCVRs 110-1 and 112-1, the couplers 110-2 and 112-2, and the antenna 110-3. In some embodiments, one or more amplifiers (e.g., a high power amplifier) could be included in the HF1 and HF2 systems 110 and 112 and connected to the coax cable to overcome cable losses, where a cable loss could be a loss of a signal's power that may be proportional to the length of the coax cable and/or attributable to one or more cable connectors employed along the cable.
The VHF1, VHF2, and VHF3 systems could include a plurality of units configured to facilitate two-way, short-range communications between the aircraft and, for example, one or more other aircraft and/or one or more ground stations. In some embodiments, the VHF1 system 114 could include a VHF1 XCVR 114-1 and a VHF1 antenna 114-2; the VHF2 system 116 could include a VHF2 XCVR 116-1 and a VHF2 antenna 116-2; and the VHF3 system 118 could include a VHF3 XCVR 118-1 and a VHF3 antenna 118-2.
As observed, RF signals may be transmitted and received between the XCVRs 114-1, 116-1, and 118-1 and their respective antennas 114-2, 116-2, and 118-2 through coax cable. In some embodiments, one or more amplifiers could be included in the VHF1, VHF2, and VHF3 systems 114, 116, and 118 and connected to the coax cable to overcome cable losses.
The remote SATCOM system 120 could include a plurality of units configured to facilitate two-way, satellite communications between the aircraft and, for example, one or more other aircraft and/or one or more ground stations. In some embodiments, the remote SATCOM system 120 could include a satellite data unit (SDU) 120-1 and a SATCOM antenna 120-2. As observed, RF signals may be transmitted and received between the SDU 120-1 and the antenna 120-2 through coax cable (or a plurality of parallel coax cables). In some embodiments, one or more amplifiers could be included in the SATCOM system 120 and connected to the coax cable (or a plurality of parallel coax cables) to overcome cable losses.
In the field of aviation, many components may be referred to as line replaceable units (LRU), portable modules designed to be removed and installed with relative ease. For the purpose of illustration, the electronic LRUs for the network 100 could include the XCVRs 110-1, 112-1, 114-1, 116-1, and 118-1; the couplers 110-2 and 112-2; the SDU 120; and the AMU 122. LRUs allow aircraft maintenance personnel to quickly remove and replace electronic equipment (i.e., those LRUs in which a plurality of electronic printed circuit boards could be installed) of aircraft systems, thereby facilitating maintenance.
ARINC 600 standard entitled “Air Transport Avionics Equipment Interfaces” is an aviation standard in which aircraft electronic equipment racking, power, and environmental packaging or form factors for LRUs have been developed and includes connector standards, mating, and support tray hold down techniques; this reference is incorporated herein in its entirety. ARINC 600 sets forth a definition, guidance, and appraisal for design and acceptance of the mechanical, electrical, and environmental interfaces between LRUs and the racks or cabinets in which they are installed. Owners and/or operators of aircraft benefit from cost savings of standardization by allowing for simpler upgrades of systems and faster replacement times of LRUs that are fundamental for the operation of an aircraft. The environmental packaging or form factor specific to each LRU may be stated in an ARINC standard applicable to the LRU to which the LRU has been functionally or operationally designed. For example, the XCVRs 114-1, 116-1, and 118-1 may be designed to the standards published in ARINC 716-11 entitled “Airborne VHF Communications Transceiver”, or ARINC 750-4 entitled “VHF Data Radio,” both of which are known to those skilled in the art.
To facilitate maintenance, electronic LRUs may be installed on support trays affixed to shelves of an electronics rack 124 in a centralized location(s) colloquially referred to as an electronic or equipment bay (E/E bay) 126. Referring now to FIG. 3 an exemplary shape and installation configuration of the electronics rack 124 is shown. As observed, the electronics rack 124 provides a centralized location where a plurality of LRUs (shown with dotted and diagonal fill patterns) of a plurality of aircraft systems may be installed on support trays 128 affixed to shelves 130 of an electronics rack 124. As observed, XCVRs 110-1, 112-1, 114-1, 116-1, and 118-1, SDU 120-1, and AMU 122 (shown with the dotted fill patterns).
The ambient temperature within an E/E bay may become hot due to a buildup of heat collectively generated and dissipated by the plurality of centrally located electronic LRUs. Without adequate ventilation and/or cooling air, one or more LRUs could easily exceed maximum operating temperatures to which they are designed and certified, and/or could operate at higher temperatures which may result in reduced LRU reliability. ARINC 600 includes standards for the application of forced cooling air to the LRUs installed on the rack(s). Form factors of LRUs may include openings to one or more sides of the LRUs, thereby exposing the internal components such as printed circuit boards to the forced air and providing adequate ventilation for the dissipation of heat from those components.
Because the LRU's may be centrally located, wires and other transmitting means of signal and data are routed from many locations in the aircraft to the electronics rack 124. As such, the lengths of the coax cable may vary greatly among systems. For example, compare exemplary lengths of coax cables of an Airbus A320 aircraft that could be configured with the HF1 system 110, the HF2 system 112, and the VHF1 system 114. The HF1 system 110 could employ a total of approximately 107 feet of coax cable (comprised of two cables connected together at a connector having approximate lengths 40 feet and 67 feet) running in between the XCVR 110-1 and the coupler 110-2, and the HF2 system 112 could employ a total of approximately 103 feet of coax cable (comprised of two cables connected together at a connector having approximate lengths 37 feet and 66 feet), whereas the VHF1 system 114 could employ a total of approximately 29 feet of coax cable (comprised of two cables having approximate lengths 4 feet and 25 feet and connected together at a connector) running in between the XCVR 114-1 and the antenna 114-2. Depending on the type of cable employed, the weight of coax cable may vary between five and fourteen pounds per one-hundred feet. For the HF1 system 110, the approximate weights attributable to the coax cable could range between 5.35 and 15 lbs., whereas the VHF1 system 114 could range between 1 and 4 lbs. Also, heavier cable could require hardware for attaching the cable and/or cable harness made up a more than one wire as well as a cable outing requiring a larger bending radius.
While the use of LRUs and a centralized location facilitates aircraft maintenance, some of wiring connected to the LRUs may have to travel from other locations in the aircraft. If an LRU is a unit of a communications, navigation, and/or surveillance system which employs an antenna, relatively heavy coaxial (coax) cables may be utilized to provide a transmission path for radio frequency (RF) signals. If the distance of the cable run is relatively long, not only does weight of the aircraft increase but also heavier, more powerful amplifiers have to be used to overcome a loss of signal power caused by coax cable propagation.